Journal of Applied Crystallography

Volume 46, Part 1 (February 2013)

Cover illustration: A schematic of a new X-ray scattering geometry, grazing-incidence transmission small-angle X-ray scattering. The incident beam impinges on the edge of a nanostructured surface at a grazing angle, and exits through the sample's edge. The method is demonstrated for gratings where it is shown that the Born approximation is valid with a simple and small correction. Courtesy of Lu et al. [J. Appl. Cryst. (2013), 46, 165-172].

Implementation and performance of SIBYLS: a dual endstation small-angle X-ray scattering and macromolecular crystallography beamline at the Advanced Light Source

Synopsis: The SIBYLS beamline of the Advanced Light Source at Lawrence Berkeley National Laboratory is a dual endstation small-angle X-ray scattering and macromolecular crystallography beamline. Key features and capabilities are described along with implementation and performance.

High-pressure phase transitions and equations of state in NiSi. III. A new high-pressure phase of NiSi

Synopsis: A new orthorhombic high-pressure phase of NiSi has been synthesized in a multi-anvil press at 1223-1310 K and 17.5 GPa. Its crystal structure has been determined and found to be closely related to that of a tetragonal form of NiSi predicted previously to be stable at high pressure by ab initio computer simulations.

Improvement of crystal quality for tetragonal hen egg white lysozyme crystals under application of an external alternating current electric field

Synopsis: It has been observed that the FWHMs of X-ray rocking-curve profiles for crystals grown with an external electric field are smaller than those for crystals grown without. These results indicate that the crystal quality of hen egg white lysozyme crystals could be improved by application of an external alternating current electric field during growth.

Synopsis: In a proof-of-principle polarized neutron Laue diffraction experiment it is shown that the featureless incoherent background due to hydrogen can be uniformly reduced by means of dynamic nuclear polarization of the proton spins, while the intensities of the Laue reflections can be enhanced or diminished significantly.

Synopsis: The ordering of carbon vacancies induces the reduction of twinning interfacial energy and leads to the presence of {111} twinning structures in nonstoichiometric ZrC0.6. Two types of twinning boundaries, i.e. {111}C and {111}Zr, can be recognized.

Contrast in transmission X-ray diffraction topographs of growth defects in the core of SrLaGaO4 single crystals

Synopsis: Defects in the core of SrLaGaO4 single crystals were studied by transmission X-ray diffraction topography. The contrast of the defect images was analysed for various diffraction conditions and as a function of absorption. The results of the analysis confirm the model of crystal lattice deformation around rod-like volume defects in SrLaGaO4 crystals.

Dislocation densities and prevailing slip-system types determined by X-ray line profile analysis in a textured AZ31 magnesium alloy deformed at different temperatures

Synopsis: The substructure in terms of dislocation densities and prevailing slip-system types is determined by the method of X-ray line profile analysis in two different texture components of an AZ31-type Mg-base alloy after extrusion and subsequent tensile deformation at different temperatures.

Synopsis: The concept of the directional pair distribution function is proposed for an atomistic level interpretation of the line profile broadening in powder diffraction patterns of nanocrystalline materials.

Normalized structure factor analysis with the CentroMK program

Synopsis: The ideal asymptotic probability density function and the exact probability density function of the normalized structure factor are compared and a program for normalized structure factor analysis is described.

Cimetidine, C10H16N6S, form C: crystal structure and modelling of polytypes using the superspace approach

Synopsis: An efficient method for modelling a polytypic family is presented with the example of cimetidine in the form C polymorph. The method exploits the (3 + 1)-dimensional superspace model, which is a powerful tool for the description, prediction and understanding of polytype modifications in small-molecule crystallography, as illustrated with this pharmaceutical example.

Experience with exchange and archiving of raw data: comparison of data from two diffractometers and four software packages on a series of lysozyme crystals

Synopsis: A systematic analysis of diffraction data of 11 different lysozyme crystals (used for cisplatin and carboplatin binding studies), obtained with four diffraction data processing software packages and from two different diffractometers, serves as a pilot study for archiving raw diffraction data and associated metadata. The availability of the raw diffraction images allows for independent assessment of software packages.

Study of threading dislocation density reduction in AlGaN epilayers by Monte Carlo simulation of high-resolution reciprocal-space maps of a two-layer system

Synopsis: High-resolution X-ray diffraction in coplanar and noncoplanar geometries has been used to investigate the influence of an SiNx nano-mask in the reduction of the threading dislocation density of high-quality AlGaN epitaxial layers grown on sapphire substrates.

Some properties of the neutron monochromatic beams obtained by multiple Bragg reflections realized in bent perfect single crystals

Synopsis: A new type of high-resolution neutron monochromator based on multiple reflections realized in bent perfect crystals of Si and Ge was tested. By means of multiple reflections, a highly collimated and simultaneously highly monochromatic beam of rather large cross section can be obtained.

Crystallographic relations during decomposition of the ferritic phase by isothermal ageing of duplex stainless steel

Synopsis: Orientation relations between the ferritic, austenitic and -phase grains in duplex stainless steels were converted into mathematical (matrix) expressions and these expressions were confirmed by automated electron backscatter diffraction measurements of the orientations of single grains.

Synopsis: Improved data collection and analysis strategies concerning the `pencil-beam' synchrotron X-ray diffraction tomography technique have been used to obtain quantitative information about the spatial distribution and time evolution of all the phases present in complex systems, such as hydrated cement samples.

Synopsis: The underlying techniques and capabilities of submicrometre-resolution three-dimensional X-ray microscopy (3DXM) are reviewed. The major applications and accomplishments of 3DXM are discussed through selected examples, including investigations of local elastic strain, plastic strain, crystal structure, phase changes and microstructure evolution.

Grazing-incidence transmission X-ray scattering: surface scattering in the Born approximation

Synopsis: A new scattering geometry, grazing-incidence transmission small-angle X-ray scattering, is introduced. With this geometry the incident beam is at a grazing angle well above the critical angle and the scattered beam exits through the edge of the substrate. This geometry validates the Born approximation.

Advances in exploiting preferred orientation in the structure analysis of polycrystalline materials

Synopsis: Improvements to the experimental setup, the data collection strategy and the data analysis procedure have simplified the method for exploiting preferred orientation in the structure analysis of polycrystalline materials.

Formation of (Fe,Cr) carbides and dislocation structures in low-chromium steel studied in situ using synchrotron radiation

Synopsis: The evolution of the size distribution of (Fe,Cr) carbides and the dislocation structure in low-chromium steel is studied during quenching and rapid heating by in situ small-angle X-ray scattering (SAXS). From simulations based on the theory of SAXS from dislocations, it is shown that the measured streaks in the two-dimensional SAXS patterns correspond to a dislocation structure of symmetric low-angle tilt boundaries, which in turn corresponds to the crystallographic orientation gradient in the single crystal of ferrite as measured by three-dimensional X-ray diffraction microscopy.

Short-range and long-range order of phyllomanganate nanoparticles determined using high-energy X-ray scattering

Synopsis: High-energy X-ray scattering data from turbostratic phyllomanganate nanosheets are analyzed in real-space by pair distribution function analysis and in reciprocal space by the Bragg-rod method and the Debye equation. The elastic deformation of the two-dimensional nanocrystals is modeled with (1) a new empirical strain function in Bragg-rod calculations and (2) explicit spherical and cylindrical mandrels implemented in the Debye equation.

Twin and topotactic growth of -eucryptite dendrites and their lattice coincidence analysed by the reticular theory

Synopsis: The crystallographic orientation of -eucryptite dendrites has been analysed by the electron backscatter diffraction technique, and a twin relationship and a topotactic relationship between dendrites have been found. The twin index n = 2 and the obliquity = 3.2877°.

On the determination of the helical structure parameters of amyloid protofilaments by small-angle neutron scattering and atomic force microscopy

Synopsis: Various models to describe small-angle neutron scattering data from helices of amyloid protofilaments (hen egg white lysozyme) in solution were analyzed. The found parameters were compared with those obtained by atomic force microscopy of the dried adsorbed state of amyloid fibrils.

ABSORB-7 and ABSORB-GUI for single-crystal absorption corrections

Synopsis: ABSORB, a program to calculate and apply absorption corrections to single-crystal X-ray intensity data, has been reconfigured to allow it to be called directly from external data processing programs. ABSORB-GUI has been developed to allow much easier specification of standard experiments.

SrRietveld: a program for automating Rietveld refinements for high-throughput powder diffraction studies

Synopsis: SrRietveld, a Python-based Rietveld refinement program, is described. SrRietveld extends and automates the popular existing Rietveld programs FullProf and GSAS to facilitate studies that involve many refinements, such as the analysis of large numbers of data sets.

An X-ray diffractometer coupled with diffuse reflectance infrared Fourier transform spectroscopy and gas chromatography for in situ and in operando characterization: an innovative analytical laboratory instrument

Synopsis: An innovative analytical tool combining X-ray diffraction, diffuse reflectance infrared Fourier transform spectroscopy and gas chromatography using a dedicated reaction cell for in situ and in operando characterization has for the first time been developed for laboratory-scale application. The use of this multitechnique device is illustrated by the study of the thermal decomposition of calcium oxalate.

Effect of crucible design on crystalline perfection and the enhanced optical properties of benzimidazole single crystals grown by the vertical Bridgman technique

Synopsis: The reported investigations reveal that the crystalline perfection and optical properties of crystals grown by the vertical Bridgman technique with a specially designed double-walled ampoule are better than those of the usually used single-walled ampoule-grown crystals.